An analogue mixer can be useful but I wouldn't say it was an advantage except if the preamps in your converter aren't very good at high gain. In that case, if you've already got a mixer with better preamps you can use that. If you don't have a mixer already, that money would be better spent on standalone preamps or a better converter.
Having said that, a mixer is useful. I use my mixer to EQ the input and output of my outboard reverbs. I'll sometimes use it to submix some inputs down to stereo if I'm running short of inputs on the DAW.